Of the many printing methods that are currently in use, the four methods most prevalent today are letterpress, flexography, gravure, and offset lithography, or offset printing. The total worldwide market for the printing industry is currently estimated to be $420 billion, with offset and gravure printing comprising the majority of that market with approximately 47% and 20% of the total volume, respectively.
Gravure is an intaglio printing process. The printer's image carrier is commonly called a “printing plate”; however, it is most typically a hollow metal cylinder covered with many tiny indentations known as “cells” that transmit the printed image. During printing, the image carrier is immersed in fluid ink. As the image carrier rotates, ink fills the etched cells that cover the surface of the cylinder. The surface of the cylinder is then wiped with a squeegee known as a “doctor blade” that leaves the non-image area clean while retaining the ink in the recessed cells. During the process of printing, paper is brought into contact with the image carrier with the help of an impression roll that applies pressure. At the point of contact, ink is drawn out of the cells of the image carrier onto the paper by capillary action.
Gravure is a large-volume printing method. The high costs of cylinders generally limit gravure printing to run lengths of over 1 million impressions. Gravure presses are also much wider, and therefore more expensive, than other printing press types. Unlike the inks used in letterpress or offset printing, the ink used in gravure printing is very fluid and is usually solvent-based; as a result, the ink is an environmental hazard. In addition, the method of cutting cells into the image carrier is typically a photolithographic process in which the cell patterns are etched into a copper-clad image carrier using highly corrosive and toxic chemicals. What is needed is a lower-cost method of producing gravure image carriers that reduces or eliminates the environmental and human risks associated with the current methods that use chemical etching.
An example of an improved method of producing gravure image carriers is described in U.S. Pat. No. 4,405,709, “Process for fabricating gravure printing plate blank.” The '709 patent describes a reusable gravure cylinder blank that can be readily processed into an image carrier. The blank includes a non-etchable and wear-resistant layer of chromium that overlays the surface of the cylinder. In addition, multiple dot-like “etchable” portions of copper, of equal size and uniform placement, are also located on the surface of the cylinder. The copper dots are isolated from each other by the non-etchable chromium. The gravure printing image carrier or printing cylinder is produced from this blank by a selective etching process that removes some of the etchable copper dots. In this way, the use of copper and, therefore, the costs of producing an image carrier are reduced. In addition, the use of toxic etching chemicals is greatly reduced, in comparison with standard techniques.
Although the method of the '709 patent reduces costs by reducing the etching of copper, it does not eliminate the etching of copper and other expensive materials. In addition, the use of chemical etching agents is reduced, but not eliminated. What is needed is means of producing a gravure printing cylinder that does not rely on etching and does not use hazardous chemicals. The present invention fulfills this need.